I don't know about this specific thing, but in some cases with "what ifs" on projects, it's more a case of whomever made it simply hoping/considering the Beach Boys rather than a plan having ever actually been in place to do it.
I have to wonder if they reconsidered once they looked up the Beach Boys in 1978 and found that the guys that would be singing the song in the movie would look something like this:
Maybe I'm missing something, but I don't think all of the guys would have shaved the facial hair and done themselves up to look like late 1950s dudes.